A series of behavioral checklists, administered to the parent, were used to characterize young girls with Fragile X Syndrome as well as a comparison group of developmentally delayed girls known to test negative fro Fragile X. These included the Conners and Autism Checklists. The purpose of this project is to assess the relationship of the behavioral dimensions measured through these instruments, particularly hyperactivity and autism measures, with age and IQ, and to compare these relationships for the two groups. Results to date indicate a nonlinear relationship between age and IQ status, suggesting potential, nonadditive, effects of developmental stage and severity. Further goals currently being pursued include the development of predictive models for potential use in screening to identify individuals likely to have Fragile X Syndrome in developmentally delayed populations, with the aim of identifying candidates for DNA testing.